Ferromagnetic material



1962 J- H. WERNICK 3,065,071

FERROMAGNETIC' MATERIAL Filed March 29, 1961 //v l/ENTOR J h. WE RN/ CK ATTORNEY United States Patent Oilfice 3,065,97i Patented Nov. 26, 1962 This invention relates to a new ferromagnetic composition. This composition, essentially the ternary compound, MnAlGe, is especially effective for use in permanent magnets.

It has been found that a new and novel composition, MnAlGe, provides unexpected and significant magnetic properties. Specifically, this material exhibits a high degree of crystalline anisotropy, a high coercive force and an impressive saturation moment. Such properties are especially suitable for a permanent magnet material.

Crystals of MnAlGe, easily obtainable from a stoichiometric melt, have a tetragonal structure belonging to the space group D -P i/nmm. The easy magnetization axis is the c-axis.

To measure the magnetic properties of this material a sample was prepared as follows:

Lumps of each constituent approximately 4" in size were mixed in the following proportions: 18.31 gms. Mn, 8.993 grns. Al and 24.20 gms. Ge and were placed in a quartz crucible and heated in an argon atmosphere in an induction furnace to approximately 1200 C. The melt was allowed to cool to room temperature. The resulting ingot was a single phase ternary compound showing the crystal habit referred to above. The melting point of the compound was approximately 800 C. It was found that the crystal form and resulting composition were essentially unaffected by the cooling rate. Quenching the melt in water produced essentially the same crystal habit.

The ingot obtained was then milled in a ball mill to an average particle size of approximately 400 microns. These particles were dropped into a quarter inch capsule containing molten parafiin and were then ferromagnetio ally aligned with a field of 3,000 gauss. The capsule was allowed to cool until the paraffin solidified and the coercive force of the resulting sample was measured. The particles were found aligned in the field and the easy axis of magnetization (the c-axis) was parallel to the field direction. The observed coercive force was 2,200

oersteds. The following specific characteristics were found:

Table I Saturation magnetization (41TM 3600 gauss. Anisotropy constant K; 5.3-10 ergs% em Maximum calculated coercive force 36,00 oersteds. Observed coercive force from above sample) 2,200 oersteds. Estimate of the maximum theoretical energy product 7.1O gauss-oersteds.

The anisotropy constant was calculated from an extrapelation of the data appearing in the figure.

The figure is a pint the magnetization in gauss per gram vs. H, the applied field in oersteds.

Referring to the figure, curveAshows the magnetization curve for a single crystal with the field H along the c-axis, the easy direction of magnetization. Curve B shows the magnetization curve for the crystal aligned with the field H perpendicular to the easy direction. Curve B, extropolated to intersect curve A gives a crystalline anisotropy field or maximum theoretical coercive force of 36,000 oersteds and a saturation magnetization 47rM =3600 gauss. The anisotropy constant is calculated using the formula:

where H is the anisotropy field (oersteds), M is the saturation moment, and K is the first anisotropy constant in ergs/cm. The saturation moment is obtained from the relation:

where B-H is the saturation magnetization in the easy direction.

Whereas the observed coercive force for the sample measured was 2200 gauss, higher coercive forces may be obtained by using smaller magnetic particles and ferromagnetically aligning them in stronger fields.

Various modifications in the molecular composition MnAlGe can be tolerated Without a significant departure in useful magneto properties of the material. A 10 atomic ercent deficiency in manganese was found to produce only a 5% reduction in saturation magnetization and, assuming a nearly linear function, a 20% variation in atomic proportion of Mn results in a 10% reduction in saturation magnetization. Excessess in manganese were found to exhibit a similiar effect. Varations in atomic per centages of aluminum and germanium produced essentially the same departures in optimum magnetic properties as those observed with modifications in manganese content.

Thus, a composition can be established which includes such variations in composition and still affords substantial magnetic properties. Departures from the basic ternary composition result in excessive deficiencies in magnetic properties when they exceed the following limits:

For many purposes more preferred limits are respresented by:

While these representations appear as molecular formulas, the subscripts should be considered to be atomic ratios and not as representing an absolute number of atoms. Thus, the representations Mn AL Ge designates a composition having the given atomic propertions of each constituent and not a molecule deficient in atoms. Based on weight percentage composition of each constituent in the above ranges of atomic proportions, the composition is expressed as:

Pecent Mn 26.6-44.7 Al- 12.5-24.3 Ge 37.5-57.3

and preferably:

Precent Mn 31.1-39.7 Al 15.1-20.6 Ge 42.6-51.6

3 2. A ferromagnetic composition consisting essentially of a mutual solid solution having atomic proportions indicated by the formula:

M .9-1.1 .9-1.1 .9 1.1 3. A ferromagnetic composition consisting essentially of by Weight:

Percent Manganese 26.644.7 Aluminum- 12.524.3 Germanium 37.557.3

4. A ferromagnetic composition consisting essentially of by Weight:

Percent Manganese 31.1-39.7 5 Aluminum 15.1-20.6 Germanium 42.651.6

References (Ziteti in the file of this patent UNITED STATES PATENTS 10 2,844,737 Hahn et al. July 22, 1958 

3. A FERROMAGNETIC COMPOSITION CONSISTING ESSENTIALLY OF BY WEIGHT: 